Method, system, and program for remote copy in an open systems environment

ABSTRACT

Disclosed is a method, system, program, and data structure for providing a shadow copy of data storage areas in a primary site to data storage areas in a secondary site. A definition is made of storage areas in the primary site having data to be shadowed and corresponding storage areas in the secondary site to shadow data at the storage areas in the primary site. A shadow pair comprises one primary storage area and one secondary storage area that shadows data for the primary storage area in the pair. A standard data transfer interface protocol command, such as a SCSI or Fibre Channel command, is used to configure status storage areas in the secondary site to provide status information and data for each primary and secondary storage area. A write command in the standard data transfer interface protocol is then used to write status information to the status storage areas indicating status of the shadowed data at the secondary storage areas in the pairs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending andcommonly-assigned patent applications, all of which are filed on thesame date herewith, and all of which are incorporated herein byreference in their entirety:

“Method, System, And Program For Selecting One of Multiple Paths toCommunicate With a Device”, to David A. Burton, Robert L. Morton, andErez Webman, U.S. patent application Ser. No. 09/591,024, currentlypending ,and “Method, System, And Program For Determining A Number ofWrite Operations to Execute” to David A. Burton, Robert L. Morton, andErez Webman, U.S. patent application Ser. No. 09/591,023, currentlypending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system, method, and program forshadowing data at a remote site and, in particular, shadowing data in anopen systems environment.

2. Description of the Related Art

Data storage systems often include a data protection component thatinvolves creating a back-up copy of data to use in the event of a systemfailure. One such data protection system involves the use of a computerat a remote site, often referred to as the secondary system, shadowingdata storage at a primary site having a primary computer and storage. Ifthere is a system failure at the primary site, then the data can berecovered from the secondary site. One such disaster recovery systemthat provides data shadowing is the International Business MachinesCorporation (IBM) Peer-to-Peer Remote Copy (PPRC) system. In a PPRCsystem, a primary storage controller provides access to a primary massstorage systems, such as one or more Direct Access Storage Devices(DASDs), comprised of interconnected hard disk drives. The storagecontroller manages the flow of data from host systems to DASDs. Asecondary controller provides a shadow copy of designated volumes in theprimary DASD in a secondary mass storage system. A high speed dedicatedline, such as Enterprise System Connection (ESCON) channels **, may beused to transfer data from the primary controller to the secondarycontroller. In PPRC systems, a relationship is established betweenvolumes in the primary DASD and the secondary DASD by copying thedesignated volumes from the primary DASD to the secondary DASD throughthe primary and secondary controllers. After the establishment phase,any updates to the protected volumes in the primary DASD are copied overto the secondary controller and DASD to synchronize the datatherebetween.

**Enterprise Storage Server and ESCON are registered trademarks andFibre Channel Raid Storage Controller is a trademark of IBM; Windows andWindows NT are registered trademarks of Microsoft Corporation.

Current data shadowing systems require that both the primary andsecondary control unit include special purpose data shadowing firmwareor software to implement the data shadowing relationship between aprimary and secondary controllers, such as the IBM PPRC and XRC softwareand firmware. In such systems, typically, the controllers involved inshadowing customer data are from the same vendor.

Many computer networks operate in an open system environment andtransfer data using the Small Computer System Interface (SCSI) or FibreChannel architectures. In an open system environment, systems may befrom different vendors and would not communicate using special, vendorspecific protocols, such as PPRC or XRC. Thus, there is a need toprovide data shadowing in an open systems environment where the systemsdo not include special purpose firmware or software to implement suchdata shadowing.

SUMMARY OF THE PREFERRED EMBODIMENTS

To overcome the limitations in the prior art described above, preferredembodiments disclose a method, system, and program for providing ashadow copy of data storage areas in a primary site to data storageareas in a secondary site. A definition is made of storage areas in theprimary site having data to be shadowed and corresponding storage areasin the secondary site to shadow data at the storage areas in the primarysite. A shadow pair comprises one primary storage area and one secondarystorage area that shadows data for the primary storage area in the pair.A standard data transfer interface protocol command, such as a SCSI orFibre Channel command, is used to configure status storage areas in thesecondary site to provide status information and data for each primaryand secondary storage area. A write command in the standard datatransfer interface protocol is then used to write status information tothe status storage areas indicating status of the shadowed data at thesecondary storage areas in the pairs.

In further embodiments, an update from a host to one storage area in theprimary site in one shadow pair to update is received. The write commandin the standard data transfer interface protocol is then used to writethe update to the storage area for the pair to update.

Preferred embodiments provide a methodology for allowing a remotecontroller in an open systems environment to function as a secondarysite to shadow data at a primary site. Preferred embodiments allow theprimary controller to use a standard data transfer interface protocol,such as SCSI or Fibre Channel Protocol (FCP), to place statusinformation and data at the secondary site on the state of data beingshadowed. In the event of a failure at the primary site, another systemcan use the status information to determine the consistency of the dataat the secondary site in shadowing the data at the primary site. Withthe preferred embodiments, the secondary controller does not includespecial purpose data shadowing because the primary controller usesstandard data transfer protocols to maintain data shadowing status atthe secondary site.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a block diagram illustrating a computing environment in whichpreferred embodiments are implemented; and

FIGS. 2-5 illustrate logic implemented in a primary controller andremote copy host to implement the data shadowing in accordance withpreferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments of the present invention. It is understood that otherembodiments may be utilized and structural and operational changes maybe made without departing from the scope of the present invention.

FIG. 1 illustrates a computing environment in which preferredembodiments are implemented. Hosts 4 a, b may comprise any computingdevice known in the art, including servers through which other clientcomputers can access storage or clients. The hosts 4 a, b each includeat least one adaptor, such as a Fibre Channel or Small Computer SystemInterface (SCSI) adaptor card or any other network adaptor card known inthe art. The host adaptors allow the hosts 4 a, b to communicate withstorage controllers 6 a, b via switch 8. The switch 8 may comprise theIBM Fibre Channel Storage Hub or Switch, the IBM SAN Fibre ChannelSwitch, or any other switching device known in the art. A primary siteincludes a primary controller 6 a and primary storage 10 a. Designatedvolumes in the primary storage 10 are transferred to a secondary sitecomprising a secondary controller 6 b and secondary storage 10 b. Thestorage devices 10 a, b may comprise a DASD or any other non-volatilestorage device and system known in the art.

Preferred embodiments are implemented in an open systems environmentwhere the primary and secondary controllers 6 a, b and hosts 4 a, b maycomprise different types of systems from different vendors thatcommunicate using a common protocol such as SCSI or Fibre ChannelProtocol (FCP). Thus, the hosts 4 a, b and controllers 6 a, b mayinclude any operating system known in the art, including the MicrosoftCorporation Windows and NT operating systems or any other specializedoperating system.** In such open systems environment, the primarycontroller 6 a can use commonly used write commands, such as SCSI writecommands, to copy the primary volumes to the secondary volumes in thesecondary storage 10 b. In such open system embodiments, the secondarycontroller 6 b does not need special purpose software to coordinate theshadowing activities with the primary controller 6 b as the primarycontroller 6 a accomplishes the shadowing by using standard interfaceprotocol write commands. In such open systems, the primary and secondarycontrollers 6 a, b may comprise any controller device known in the artand the primary and secondary controllers 6 a, b may be of differentmodels and model types, and even of different classes of storagecontrollers.

**Enterprise Storage Server and ESCON are registered trademarks andFibre Channel Raid Storage Controller is a trademark of IBM; Windows andWindows NT are registered trademarks of Microsoft Corporation.

To ensure data consistency, both the primary 6 a secondary 6 bcontrollers maintain a state LUN 12 a, b indicating their view of thestate of shadowing data between the primary and secondary 6 a, bcontrollers. In the event of a failure of the primary controller 6 a,the hosts 4 a, b can query the state LUN 12 b at the secondarycontroller 6 b to determine the consistency of the data being shadowedbetween the primary and secondary controllers 6 a, b. In preferredembodiments, state information is maintained for each LUN pair beingshadowed between the primary 10 a and secondary 10 b DASDs, to allowdata consistency to be determined on a LUN by LUN basis. The state LUNs12 a, b are created during the establishment phase. Below are fourpossible states that may be indicated in the state LUNs 12 a, b:

Simplex: This is the state before the establishment of a remote copyrelationship between LUNs and after the remote copy session hasterminated. Simplex means that the LUN is not currently involved in datashadowing. Ending a remote copy relationship between the primary andsecondary LUNs returns the two devices to the simplex state.

Duplex Pending: The state during the establishment phase where data isinitially being copied from the primary LUN to the secondary LUN, buthas not yet completed. At this point, data is not consistent between theprimary and secondary LUNs, and the remote copy at the particularsecondary LUN cannot be used. The establishment phase ends when all thedata in the primary LUN has initially been copied over.

Full Duplex: The primary and secondary LUN pair are consistent exceptfor current writes to the primary LUN received at the primary controller6 a.

Suspend Duplex: Changes to the primary LUN have not been communicated tothe secondary LUN. The suspend state occurs when only one of the devicesin a dual copy or remote copy LUN pair is being updated because ofeither a permanent error condition or an authorized user command. Allwrites to the remaining functional device are logged. This allows forautomatic resynchronization of both LUNs when the LUN pair is reset tothe duplex state. If suspend duplex is the state during theestablishment phase where data is copied for the first time between theprimary and secondary LUNs in the DASDs 10 a, b, then the data is notconsistent as the initial copy has not completed. However, if suspendduplex is the state after the initial establishment copy has completed,then the data at the secondary LUN is consistent, but not up-to-date, asrecent writes were not communicated to the secondary LUN.

In preferred embodiments one or more hosts, e.g., host 4 a for purposesof this discussion, would include a remote copy program 14 (shown inFIG. 1) that allows the host 4 a to participate in remote copyoperations as a remote copy host. The remote copy host 4 a would executethe remote copy program 14 to query the secondary state LUN 12 b in theevent of a failure to determine the extent to which shadowed data at thesecondary LUNs may be used to recover the failed primary LUNs. Inpreferred embodiments, the secondary state LUN 12 b is configured in aredundant array of independent disks (RAID) to ensure that the stateinformation is not lost in the event of a single drive failure in thesecondary DASD 10 b.

FIG. 2 illustrates logic implemented in software and/or firmware of theprimary controller 6 a to establish a relationship between primary LUNsin the primary DASD 10 a and second LUNs in the secondary DASD 10 b toprovide a remote copy or data shadowing for the primary LUNs involved inthe relationship. As discussed, before the secondary site can startshadowing updates to the primary site, a relationship of primary LUNs inthe primary DASD 10 a and secondary LUNS in the secondary DASD 10 b mustbe established. Control begins at block 100 with the primary controller6 a initiating the establishment phase between LUN pairs, LUNs to beshadowed in the primary DASD 10 a and the corresponding secondary LUN inthe pair that will shadow the data. At block 102, the primary controller6 a configures a state LUN 12 b in the secondary DASD 10 b to include asector for each LUN in the secondary DASD 10 b. In preferredembodiments, the primary controller 6 a uses the vendor specificconfiguration commands for the secondary controller 6 b to configure thestate LUN 12 b in the secondary DASD 10 b. In preferred embodiments, theprimary controller 6 a would send these vendor-specific configurationcommands through the Fibre Channel device driver. The primary controller6 a would further configure a primary state LUN 12 a that also maintainsa copy of the status.

The primary controller 6 a then communicates (at block 104) the locationinformation of the secondary state LUN 12 b in the secondary DASD 10 bto the remote copy host 4 a. The remote copy host 4 a would use suchinformation to access the remote copy status at the secondary site inthe event of a failure of the primary DASD 10 a. The primary controller6 a will issue (at block 106) write commands to write “simplex” statusto the LUN sectors in the primary and secondary state LUNs 12 a, bcorresponding to primary and secondary LUNs, respectively, notparticipating in remote copy LUN pairs, i.e., not involved in datashadowing operations. The primary controller 6 a will further issue (atblock 110) write commands to write “duplex pending” status to thesectors in the primary and secondary state LUNs 12 a, b corresponding toprimary and secondary LUNs, respectively, participating in remote copyLUN pairs.

For each remote copy LUN pair of a primary LUN i being shadowed by asecondary LUN j, the primary controller 6 a will issue (at block 112)write commands to write the customer data from the primary LUN i to thesecondary LUN j. The primary controller 6 a may utilize the algorithmdescribed in the co-pending application “Method, System, and Program forDetermining a Number of Write Operations to Execute,” having attorneydocket No. TUC9-2000-0015US1, which application is incorporated hereinby reference in its entirety, to manage writes to copy the data from theprimary LUN i to secondary LUN j. Upon receiving (at block 130)acknowledgment from the secondary controller 6 b that the writeoperations to LUN j completed at the secondary DASD 10 b, the primarycontroller 6 a will write (at block 132) “full duplex status” to the LUNi sector in the primary state LUN 12 a and to the LUN j sector in thesecondary state LUN 12 b. At this point, the establishment phase hascompleted and all the data from the LUNs in the primary DASD 10 ainvolved in remote copy has successfully been copied over to the LUNs inthe secondary DASD 10 b shadowing the data in the primary LUNs.

FIG. 3 illustrates logic implemented in firmware and/or software in theprimary controller 6 a to shadow updates to LUNs in the primary DASD 10a that are part of a remote copy LUN pair, i.e., being shadowed on thesecondary DASD 10 b. Control begins at block 150 with the primarycontroller 6 a receiving an update to LUN i in the primary DASD 10 athat is part of a remote copy LUN pair, being shadowed by LUN j in thesecondary DASD 10 b. The LUNs i and j may be the same LUN number ordifferent LUN numbers. The primary controller 6 a applies (at block 152)the updates to LUN i in the primary DASD 10 a and returns acknowledgment(at block 154) to the host initiating the write that the update iscompleted. The primary controller 6 a then issues (at block 156) one ormore writes, such as SCSI write commands, to copy the updates to LUN ito LUN j in the secondary DASD 10 b.

At block 170, the primary controller 6 a receives status on the writerequest to secondary LUN j of the updates to the primary LUN i. If (atblock 172) the status indicates that the updates were not successfullywritten to the secondary LUN j or the write otherwise failed for anyreason, including problems with the connection, then the primarycontroller 6 a issues (at block 174) an asynchronous attention status,such as a SCSI Unit Attention, that remote copy is suspended for LUN i.This informs; the host 4 a, b that initiated the write operation and allother hosts that they cannot obtain current data for LUN i from thesecondary DASD 10 b. This status is only issued once. The primarycontroller then issues (at block 178) a write command to write “suspendduplex” status to the LUN i and LUN j sectors in the primary 12 a andsecondary 12 b state LUNs, respectively. At this point, the hosts 4 a, bcan still write updates to LUN i. However, the asynchronous attentioninforms the hosts 4 a, b that they cannot rely on the secondary DASD 10b to provide current data. Otherwise, if the updates were successfullywritten to secondary LUN j, then the logic ends.

If, at block 200, the primary controller 6 a receives status that thewrite of the “suspend duplex” status to the LUN j sector in thesecondary state LUN 12 b failed, then the primary controller 6 apresents (at block 202) asynchronous status to the remote copy host 4 band any other host attempting to access LUN i of a failure to updatestatus to the LUN j sector in the secondary state LUN 12 b. This informsthe hosts 4 a, b that they cannot rely on the status information for LUNi maintained in the secondary state LUN 12 b. This asynchronous statusmay be implemented in a read command the remote copy host 4 a presentsto the primary controller 6 a. The primary controller 6 a may queue thisread request and leave it outstanding until it needs to present statusto the remote copy host 4 a on a failed attempt to write “suspendduplex” status to the secondary site. The asynchronous status indicatingthe failure to update LUN j sector at the secondary site is onlypresented once to each host. Thus, the host 4 a, b receiving theasynchronous status continues to believe the secondary state LUN 12 bdoes not reflect the correct status for LUN j until it receives asubsequent status indicating otherwise.

FIG. 4 illustrates logic implemented in the remote copy program 14 toinvolve the remote copy host 4 b in the remote copy operations andassist the primary controller 14 a with remote copy. If the primarycontroller 6 a could not write the “suspend duplex” status to the LUN jsector in the secondary state LUN 12 b, then the remote copy host 4 amay try to apply the “suspend duplex” status as it may have alternativecommunication paths to the secondary DASD 10 b not available to theprimary controller 10 a. At block 250, in response to receiving theasynchronous status from the primary controller 4 a (at block 202, FIG.3), the remote copy host 4 a would issue a write to write the “suspendduplex” state to the LUN j sector in the secondary state LUN 12 b. Atblock 270, the remote copy host 4 a receives status on the write“suspend duplex” to the secondary state LUN 12 b. If the status (atblock 272) indicates that the write succeeded, then the remote copy host4 a informs (at block 274) the primary controller 4 a of the successfulwrite of the status; otherwise, the primary controller 4 a is notified(at block 276) that the write of the “suspend duplex” status failed.

FIG. 5 illustrates logic implemented as software and/or firmware in theprimary controller 6 a. Control begins at block 300 with the primarycontroller 6 a receiving a response from the remote copy host 4 bconcerning the write of the “suspend duplex” status to the LUN j sectorin the secondary state LUN 12 b. If the status was successfully updated(at block 302), then the primary controller 4 a queues (at block 304)the updates to LUN j. The primary controller 6 a would return success tothe host 4 a, b initiating the update. From the no branch of block 302or 304, control transfers to block 308 where the primary controller 6 awould periodically attempt to establish a connection with LUN j in thesecondary DASD 10 b.

As discussed, there are two possible asynchronous statuses. Oneindicates that the secondary DASD 10 b does not include current data forLUN i and the second indicates that the status for LUN i in thesecondary state LUN 12 b is not accurate. At block 330, the primarycontroller 6 a receives notification that the connection with LUN j atthe secondary site is reestablished. The primary controller 6 a thenwrites (at block 332) any queued writes for LUN j to LUN j and thenwrites (at block 334) “full duplex” status to the LUN i and LUN jsectors in the primary 12 a and secondary 12 b state LUNs, respectively.The primary controller 12 a further provides (at block 336) asynchronousstatus one time to any host providing updates to LUN j of the new statusof LUN j, i.e., that it is available and the status for LUN j in thesecondary state LUN 12 b is current.

With the preferred embodiments, in the event of a failure in the primaryDASD 10 a, the remote copy host can read the secondary state LUN 12 b todetermine the status of the secondary LUNs shadowing data. If the statusis full duplex, then the remote copy host 4 a knows that the data at thesecondary LUNs in the remote copy LUN pairs is consistent for all writesthat have completed. In preferred embodiments, hosts log updates in ajournal until they receives status that the update was successfullyapplied. In the event of a failure, for those writes that have notcompleted, the hosts 4 a, b can recover the unapplied writes from thehost journal log, and then apply those updates to the secondary LUNsinvolved in remote copy to derive the current data at the time of thefailure. If multiple hosts had outstanding writes to the primary LUNs inthe remote copy relationship, then the uncompleted updates would have tobe gathered from journal logs from all those hosts having uncompletedupdates to the primary LUNs.

If there is a failure, and the status is “duplex pending”, then the dataat the secondary LUN is not consistent because the establishment phaseof the initial copy has not completed to that particular LUN. “Suspendduplex” means that updates have not been communicated to the secondaryLUN due to a failure. In case of a failure while the secondary LUN is in“suspend duplex”, the data can be recovered from the journal logs ofhosts that have outstanding updates to the primary LUNs involved in theremote copy operation.

Preferred embodiments provide a system for allowing controllers in anopen systems environment to function as secondary controllers in aremote copy relationship to shadow data. In the preferred embodiments,the secondary controllers do not need any special purpose firmware orsoftware to participate in the data shadowing relationship. Instead, theprimary controller writes status information to the secondary DASD usinga standard data transfer interface protocol, such as SCSI or FibreChannel commands, that are acceptable by all systems in an open systemenvironment. The status information is written to the secondary DASD toallow a remote copy host or agent to determine the status of remote copyoperations at the time of the failure of the primary DASD.

Conclusion

The following describes some alternative embodiments for accomplishingthe present invention.

The preferred embodiments may be implemented as a method, apparatus orprogram using standard programming and/or engineering techniques toproduce software, firmware, hardware, or any combination thereof. Theprograms defining the functions of the preferred embodiment can bedelivered to a computer via a variety of information bearing media,which include, but are not limited to, computer-readable devices,programmable logic, memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs,SRAMs, etc.) carriers, or media, such as a magnetic storage media,“floppy disk,” CD-ROM, a file server providing access to the programsvia a network transmission line, wireless transmission media, signalspropagating through space, radio waves, infrared signals, etc. Ofcourse, those skilled in the art will recognize that many modificationsmay be made to this configuration without departing from the scope ofthe present invention. Such signal-bearing media, when carryingcomputer-readable instructions that direct the functions of the presentinvention, represent alternative embodiments of the present invention.

In preferred embodiments, one primary controller 6 a shadowed data on asingle secondary controller 6 b. However, in alternative arrangements,one primary controller may shadow data at multiple secondary controllersor multiple primary controllers may shadow data at one or more secondarycontrollers.

In preferred embodiments, data storage areas were delineated as LUNs. Inalternative embodiments, storage areas may be divided according todifferent means.

The preferred logic of FIGS. 2-5 describe specific operations occurringin a particular order. In alternative embodiments, certain of the logicoperations may be performed in a different order, modified or removedand still implement preferred embodiments of the present invention.Morever, steps may be added to the above described logic and stillconform to the preferred embodiments. Further, operations describedherein may occur sequentially or certain operations may be processed inparallel.

In preferred embodiments, the primary and secondary controllerscommunicated over a fibre channel interface using SCSI or Fibre Channelcommands. In alternative embodiments, different command protocols may beutilized. For instance, the ESCON protocol may be used for the channelcommunications and the count-key-data.(CKD) protocol may be used for theinput/output (I/O) commands.

Preferred embodiments were described with respect to a storage system inwhich data from a primary site is shadowed at a secondary site as partof a data backup and recovery system. However, the preferred method,system, and program for shadowing data may apply to non-data recoverysystems, or whenever a mirror copy of data is needed.

In summary, preferred embodiments disclose a method, system, and programfor providing a shadow copy of data storage areas in a primary site todata storage areas in a secondary site. A definition is made of storageareas in the primary site having data to be shadowed and correspondingstorage areas in the secondary site to shadow data at the storage areasin the primary site. A shadow pair comprises one primary storage areaand one secondary storage area that shadows data for the primary storagearea in the pair. A standard data transfer interface protocol command,such as a SCSI or Fibre Channel command, is used to configure statusstorage areas in the secondary site to provide status information anddata for each primary and secondary storage area. A write command in thestandard data transfer interface protocol is then used to write statusinformation to the status storage areas indicating status of theshadowed data at the secondary storage areas in the pairs.

The foregoing description of the preferred embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto. The above specification, examples and dataprovide a complete description of the manufacture and use of thecomposition of the invention. Since many embodiments of the inventioncan be made without departing from the spirit and scope of theinvention, the invention resides in the claims hereinafter appended.

What is claimed is:
 1. A method for providing a shadow copy of datastorage areas in a primary site to data storage areas in a secondarysite, comprising: defining storage areas in the primary site having datato be shadowed and corresponding storage areas in the secondary site toshadow data at the storage areas in the primary site, wherein a shadowpair comprises one primary storage area and one secondary storage areathat shadows data for the primary storage area in the pair; using astandard data transfer interface protocol command to configure statusstorage areas in the secondary site to provide status information anddata for each primary and secondary storage area; and using a writecommand in the standard data transfer interface protocol to write statusinformation to the status storage areas indicating status of theshadowed data at the secondary storage areas in the pairs.
 2. The methodof claim 1, further comprising using the write command in the standarddata transfer interface protocol to write a status to each statusstorage area providing status information for storage areas at theprimary and secondary sites not involved in data shadow operations. 3.The method of claim 1, further comprising: using the write command inthe standard data transfer interface protocol to write a first status toeach status storage area for a primary and secondary storage area pairinvolved in data shadow operations; and using the write command in thestandard data transfer interface protocol to write a second status tostatus storage areas for those primary and secondary pairs where datawas successfully copied from the storage area in the primary site to thestorage area in the secondary site.
 4. The method of claim 1, furthercomprising: receiving an update from a host to one storage area in theprimary site in one shadow pair to update; and using the write commandin the standard data transfer interface protocol to write the update tothe secondary storage area for the pair to update.
 5. The method ofclaim 4, further comprising: if the write of the update to the secondarystorage area in the pair to update did not complete, then using thewrite command in the standard data transfer interface protocol to writea suspend status to the status storage area for the pair to update;applying the update to the storage area in the primary site in the pairif the suspend status was written to the status storage area for thepair to update.
 6. The method of claim 5, further comprising: if thewrite of the suspend status failed to the status storage area, thennotifying a remote computer; using, with the remote computer, the writecommand in the standard data transfer interface protocol to write thesuspend status to the status storage area for the pair to update.
 7. Themethod of claim 6, further comprising: presenting asynchronous status ifthe suspend status or data was not written to the secondary site.
 8. Themethod of claim 7, further comprising: queuing updates that were notwritten to the storage area at the secondary site; retrying to write thequeued updates to the secondary site; and presenting further theasynchronous status after successfully writing the queued updates to thestorage area at the secondary site indicating that data at the secondarysite is current.
 9. The method of claim 1, wherein the standard datatransfer interface protocol comprises SCSI or Fibre Channel Protocol.10. A system for shadowing data: a primary site including a primarycontroller and primary storage; a secondary site including a secondarycontroller and secondary storage; means for defining storage areas inthe primary site having data to be shadowed and corresponding storageareas in the secondary site to shadow data at the storage areas in theprimary site, wherein a shadow pair comprises one primary storage areaand one secondary storage area that shadows data for the primary storagearea in the pair; means for using a standard data transfer interfaceprotocol command to configure status storage areas in the secondary siteto provide status information and data for each primary and secondarystorage area; and means for using a write command in the standard datatransfer interface protocol to write status information to the statusstorage areas indicating status of the shadowed data at the secondarystorage areas in the pairs.
 11. The system of claim 10, furthercomprising means for using the write command in the standard datatransfer interface protocol to write a status to each status storagearea providing status information for storage areas at the primary andsecondary sites not involved in data shadow operations.
 12. The systemof claim 10, further comprising: means for using the write command inthe standard data transfer interface protocol to write a first status toeach status storage area for a primary and secondary storage area pairinvolved in data shadow operations; and means for using the writecommand in the standard data transfer interface protocol to write asecond status to status storage areas for those primary and secondarypairs where data was successfully copied from the storage area in theprimary site to the storage area in the secondary site.
 13. The systemof claim 10, further comprising: means for receiving an update from ahost to one storage area in the primary site in one shadow pair toupdate; and means for using the write command in the standard datatransfer interface protocol to write the update to the secondary storagearea for the pair to update.
 14. The system of claim 13, furthercomprising: means for using the write command in the standard datatransfer interface protocol to write a suspend status to the statusstorage area for the pair to update if the write of the update to thesecondary storage area in the pair to update did not complete; means forapplying the update to the storage area in the primary site in the pairif the suspend status was written to the status storage area for thepair to update.
 15. The system of claim 14, further comprising: a remotecomputer; means for notifying the remote computer if the write of thesuspend status failed to the status storage area; means, in the remotecomputer, for using the write command in the standard data transferinterface protocol to write the suspend status to the status storagearea for the pair to update.
 16. The system of claim 15, furthercomprising: means for presenting asynchronous status if the suspendstatus or data was not written to the secondary site.
 17. The system ofclaim 16, further comprising: means for queuing updates that were notwritten to the storage area at the secondary site; means for retrying towrite the queued updates to the secondary site; and means for presentingfurther the asynchronous status after successfully writing the queuedupdates to the storage area at the secondary site indicating that dataat the secondary site is current.
 18. The system of claim 10, whereinthe standard data transfer interface protocol comprises SCSI or FibreChannel Protocol.
 19. An information bearing medium for providing ashadow copy of data storage areas in a primary site to data storageareas in a secondary site, the information bearing medium comprisingcode capable of causing a processor to perform: defining storage areasin the primary site having data to be shadowed and corresponding storageareas in the secondary site to shadow data at the storage areas in theprimary site, wherein a shadow pair comprises one primary storage areaand one secondary storage area that shadows data for the primary storagearea in the pair; using a standard data transfer interface protocolcommand to configure status storage areas in the secondary site toprovide status information and data for each primary and secondarystorage area; and using a write command in the standard data transferinterface protocol to write status information to the status storageareas indicating status of the shadowed data at the secondary storageareas in the pairs.
 20. The information bearing medium of claim 19,further causing the processor to perform using the write command in thestandard data transfer interface protocol to write a status to eachstatus storage area providing status information for storage areas atthe primary and secondary sites not involved in data shadow operations.21. The information bearing medium of claim 19, further causing theprocessor to perform: using the write command in the standard datatransfer interface protocol to write a first status to each statusstorage area for a primary and secondary storage area pair involved indata shadow operations; and using the write command in the standard datatransfer interface protocol to write a second status to status storageareas for those primary and secondary pairs where data was successfullycopied from the storage area in the primary site to the storage area inthe secondary site.
 22. The information bearing medium of claim 19,further causing the processor to perform: receiving an update from ahost to one storage area in the primary site in one shadow pair toupdate; and using the write command in the standard data transferinterface protocol to write the update to the secondary storage area forthe pair to update.
 23. The information bearing medium of claim 22,further causing the processor to perform: if the write of the update tothe secondary storage area in the pair to update did not complete, thenusing the write command in the standard data transfer interface protocolto write a suspend status to the status storage area for the pair toupdate; applying the update to the storage area in the primary site inthe pair if the suspend status was written to the status storage areafor the pair to update.
 24. The information bearing medium of claim 23,further causing the processor to perform: if the write of the suspendstatus failed to the status storage area, then notifying a remotecomputer; wherein the information bearing medium further includes codecapable of causing the remote computer to perform using the writecommand in the standard data transfer interface protocol to write thesuspend status to the status storage area for the pair to update. 25.The information bearing medium of claim 24, further causing theprocessor to perform: presenting asynchronous status if the suspendstatus or data was not written to the secondary site.
 26. Theinformation bearing medium of claim 25, further causing the processor toperform: queuing updates that were not written to the storage area atthe secondary site; retrying to write the queued updates to thesecondary site; and presenting further the asynchronous status aftersuccessfully writing the queued updates to the storage area at thesecondary site indicating that data at the secondary site is current.27. The information bearing medium of claim 19, wherein the standarddata transfer interface protocol comprises SCSI or Fibre ChannelProtocol.